Induction of circular dichroism of symmetrical porphyrins bound to random coil polypeptides in aqueous solutions

Circular dichroism spectroscopic study of non-covalent interactions of poly-L-glutamic acid with a porphyrin derivative in aqueous solutions

“…It is well known that secondary structure, which depends on intramolecular hydrogen bonds, is influenced by the physicochemical properties of solution [30] and polypeptide conformational changes have been described [14,[31][32][33][34]. Therefore, polypeptides can serve as polymeric spatially aligned matrices, which are able to imprint their geometric properties onto the interacting porphyrins [35][36][37][38][39][40]. A large induced ECD signal in the Soret region, which is characteristic for porphyrins, was observed in non-covalent complexes [37][38][39] as well as in covalent porphyrin-peptide conjugates [35].…”

“…Therefore, polypeptides can serve as polymeric spatially aligned matrices, which are able to imprint their geometric properties onto the interacting porphyrins [35][36][37][38][39][40]. A large induced ECD signal in the Soret region, which is characteristic for porphyrins, was observed in non-covalent complexes [37][38][39] as well as in covalent porphyrin-peptide conjugates [35]. The induction of porphyrin optical activity is not caused only by large macromolecules such as polypeptides but also by small chiral molecules, for example amino acids [41].…”

“…The ionic interaction between homopolypeptides and porphyrins has already been studied in systems composed of cationic poly-L-lysine and anionic mesotetrakis(4-sulfonatophenyl)porphyrin (TPPS). The porphyrin part of the complexes was characterized [37][38][39] and the structure of the oligopeptide part of the complexes was discussed [47]. Cationic porphyrins are also widely studied because of their binding to the biologically important polymer DNA [48] in which the cleavage of nucleic acids can be caused by energy transfer through the porphyrin triplet states via production of singlet oxygen.…”

“…For simplicity, this secondary structure is indicated as PPII in this paper. At acidic pH in concentrations of ∼0.01 mol/l which are suitable for ECD measurements, the αhelix conformation of PLGA was detected on the basis of a characteristic ECD signal [37][38][39]52]. At concentrations more than 10 times higher than are necessary for IR spectral study, no observations of α-helix PLGA conformation in aqueous solutions at acidic pH have been published.…”

“…The ECD technique is suitable for observation of the imprinted spatial arrangement of the porphyrin derivatives as well as for the estimation of the polypeptide secondary structure at lower concentrations. Although the induction of the porphyrin optical activity due to interaction with polypeptides was reported previously [37][38][39], the conformational changes of polypeptides after binding of porphyrins, as well as the characterization of porphyrin association during the polypeptide-porphyrin complexation, were not described thoroughly and were neglected in studies dealing with polypeptide-porphyrin interactions. In this paper, a combination of circular dichroic and absorption techniques in both the UV-vis and IR regions was shown to be a powerful tool for the study of macromolecular chiral assemblies.…”